System and method for identifying the path or devices on the path of a communication signal using (1+r(t)) amplitude modulation

ABSTRACT

A system and method of applying a known modification to a signal to enable a determination of a signal received by a first node is received directly from a second node or indirectly through a repeater. The repeater receives a primary signal and creates a secondary signal as a function of the primary signal and a known modification, wherein the known modification identifies the repeater. The primary signal is transmitted and injected with the secondary signal as the first signal to the primary receiver.

CROSS REFERENCES

This non-provisional Application claims priority benefit of co-pendingProvisional Patent Application Ser. No. 60/570,081, titled SYSTEM ANDMETHOD FOR IDENTIFYING THE PATH OR DEVICE ON THE PATH OF A COMMUNICATIONSIGNAL USING (1+r(t)) AMPLITUDE MODULATION, filed May 12, 2004, thecontents of which are herein incorporated by reference.

The present non-provisional application claims priority benefit ofco-pending provisional application Ser. No. 60/570,082, titled SYSTEMAND METHOD FOR IDENTIFYING THE PATH OR DEVICES ON THE PATH OF ACOMMUNICATION SIGNAL filed May 12, 2004, the entirety of which is herebyincorporated by reference.

This non-provisional Application claims priority benefit of co-pendingProvisional Patent Application Ser. No. 60/570,067, titled SYSTEM ANDMETHOD FOR DETECTING A MOBILE STATION OPERATING THROUGH A REPEATER,filed May 12, 2004, the contents of which are herein incorporated byreference.

BACKGROUND

Applicant's disclosure is directed generally towards a wirelesscommunications network for determining whether a signal from a mobileappliance is operated on by a repeater or other network device.

The use of wireless communication devices such as telephones, pagers,personal digital assistants, laptop computers, etc., hereinafterreferred to collectively as “mobile appliances,” has become prevalent intoday's society.

FIG. 1 shows a conventional mobile-appliance communication system havingbase stations 10 a-c for communicating with a mobile appliance 20. Eachbase station 10 contains signal processing equipment and an antenna fortransmitting to and receiving signals from the mobile appliance 20 aswell as other base stations. A Base Station Controller (“BSC”) and/orMobile Switching Center (“MSC”) 45 typically is connected to each basestation 10 through a wire line connection 41.

To meet the ever growing demand for mobile communication, wirelesscommunication systems deploy repeater stations to expand range andconcentration of coverage. In FIG. 1, a repeater 50 a, associated withbase station 10 a, is located to extend the coverage area to encompassthe back side of the mountain 1. The repeater 50 b, associated with basestation 10 c, is mounted on a building and is used to provide servicewithin the building 2.

Repeaters typically fall into two categories: (1) non-translating, alsoknown as wideband, and (2) translating, also known as narrowband. Asshown in FIG. 2 a, a non-translating repeater 250 simply passes theforward F_(f1) and reverse R_(f1) frequencies from the base station 210and mobile appliance 220 respectively to and from the repeater coveragelocation. Often wideband repeaters are “in-building” or serve limitedcoverage areas. While the description of non-translating repeaters aboveand translating repeaters below are described in reference to frequency,their operation can equally be described in terms of channels, and theuse of the term frequency should not be construed to limit the scope ofthe present disclosed subject matter.

A translating repeater assigns the mobile to a different traffic channelunbeknownst to the base station, mobile switch, MPC, and the basestation controller. As shown in FIG. 2 b, the translating repeater usesthe base station traffic channel R_(f1) for repeater 250 to base station210 communication while the mobile appliance 220 utilizes a separatefrequency R_(f2) for mobile to repeater communications. Translatingrepeaters act similarly in the forward direction using F_(f1) from thebase station 210 to the repeater station 250 and F_(f2) from therepeater station 250 to the mobile appliance 220. In both cases, theexistence of the repeater is usually transparent to the network.

The function of the repeater station can be assumed to be equivalent toconverting all signals in some received bandwidth from a Radio Frequency(RF) to some Intermediate Frequency (IF). The IF signal bandwidth isthen up-converted by suitably frequency shifting this bandwidth whileconcurrently applying both amplification and a fixed delay to thesignals.

For example, let the set of signals transmitted by N mobiles in therepeaters' input bandwidth be denoted by

${{S(t)} = {\sum\limits_{k = 1}^{N}\;{{a(k)}{x\left( {k,t} \right)}{\sin\left( {w\; t} \right)}}}},$where the signal from a given mobile is denoted by x(k, t). The signalx(k, t) is contained in the repeater bandwidth and w is the angularfrequency center of the RF bandwidth. The repeater downshifts theaggregate signal to generate

${{D(t)} = {\sum\limits_{k = 1}^{N}\;{{a(k)}{x\left( {k,t} \right)}{\sin({vt})}}}},$in which v is now representative of the center of the IF bandwidth. Theentire signal D(t) is now converted back to RF by operations that areequivalent to forming the signal

${{R\left( {t + T} \right)} = {{G{\sum\limits_{k = 1}^{N}\;{{a(k)}{x\left( {k,t} \right)}{\sin({vt})}{\cos\left( {{w\; t} - {vt}} \right)}}}} + {G{\sum\limits_{k = 1}^{N}\;{{a(k)}{x\left( {k,t} \right)}{\cos({vt})}{\sin\left( {{w\; t} - {vt}} \right)}}}}}},$in which G is the repeater gain. The last equation can be written in amore convenient, mathematical manner by noting that R(t) can be derivedfrom D(t) by writing it as R(t+T)=Re{G exp(j(w−v)tI(t))}, where Gexp(j(w−v)t) is the complex representation of the multiplicative signalintroduced by the repeater on the downshifted signal bandwidth and I(t)is the complex representation of D(t).

Essentially, the function of the repeater is to convert the RF signal toan IF signal, delay and amplify that IF signal, up-convert the signalback to RF, and transmit the signal. This is true for both translatingand non-translating repeaters.

Repeaters typically communicate with the host base station via an RFlink as shown in FIG. 3 between base station 310 and repeater 350 a.This connection allows remote operation of the repeater without physicalties back to the host base station, which is particularly advantageousin rugged or other areas where laying lines are difficult or costly.Some repeaters, generally non-translating repeaters, use a fiber opticor copper wire “tether” instead of an RF link to communicate with thehost base station as shown in FIG. 3, where base station 310 isconnected to repeater station 350 b by tether 351. RF signals are placedonto the tether at the repeater and then summed into the normal basestation antenna path at the antenna feed interface 311 at the host basestation. After integration into the normal base station antenna path,the signal from the repeater is indistinguishable to the base stationregarding its origin (e.g., from the base station antennas or from atether). In this tether architecture as well, the host base station hasno knowledge of the repeater's existence or that a call is being servedby the repeater.

Neither the base station nor the switch knows that a repeater or othernetwork device is serving a call. For example, a repeater installed asan in-building distribution system would use indoor antennas tocommunicate with the indoor handsets and an outdoor antenna tocommunicate with the host base station. In order to accomplish this,there is a need to overcome the deficiencies in the prior art byemploying a novel system and method that is capable of identifying whena mobile's signal is being received via a repeater or other networkdevice.

In view of this need, it is an object of the disclosed subject matter topresent a method for determining whether a signal is received directlyfrom the mobile or from a repeater in the communication network.

These objects and other advantages of the disclosed subject matter willbe readily apparent to one skilled in the art to which the disclosurepertains from a perusal of the claims, the appended drawings, and thefollowing detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art wireless communication system

FIG. 2 a is an illustration of the operation of a prior artnon-translating repeater station.

FIG. 2 b is an illustration of the operation of a prior art translatingrepeater station.

FIG. 3 is an illustration of a prior art wireless communication systemwith repeater stations connected with an RF link and over a tether.

FIG. 4 is a representative flow chart for the operation of a repeater inan embodiment of the present subject matter.

FIG. 5 is a representative flow chart for the operation of a networkanalysis system according to an embodiment of the present subjectmatter.

FIG. 6 is a representative flow chart for determining whether an uplinksignal is received from a repeater according to an embodiment of thepresent subject matter.

FIG. 7 is a schematic diagram of a repeater, mobile and network analysissystem according to an embodiment of the present subject matter.

FIG. 8 is a schematic diagram of a repeater with a modification circuitaccording to an embodiment of the present subject matter.

DETAILED DESCRIPTION

An important aspect of the presently disclosed subject matter is anetwork analysis system can determine when a received signal from amobile has passed through a repeater. Prior art systems do not have thiscapability and consequently treat all the signals received by the basestation as having been received directly from the target mobile. Forexample, the ability to determine if a signal from a mobile has passedthrough a repeater enables embodiments of the disclosed subject matterin a network analysis system to provide more efficient networkmanagement. The foregoing are exemplary only and shall not be used tolimit the invention. These examples and others are discussed in moredetail below.

The present subject matter relates to the case where signals can bereceived at base stations, or other receivers, either directly from themobile appliance or through a repeater. The ability to discern thedifference between direct signals and repeated signals (i.e., signalsthat arrive via a repeater) allows the network analysis system tocollect data important to system operators. In the forgoing discussionsthe subject matter will be described in terms of a network analysissystem, however as noted above, any network receiver or sensor receivinga signal from the repeaters can employ the described method.

This disclosed subject matter allows repeater identification via theinsertion of a low power, amplitude modulated RF signature based on asecond signal. This co-channel signal is generated by applying aspecific form of Amplitude Modulation (AM) to the entire repeater signalbandwidth and serves as a signature identifying that a mobile is beingserved through a particular repeater station, whose identity can beuniquely determined from the RF characteristics introduced by therepeater itself. The magnitude of the inband signal as well as anyadjacent channel interference caused by the AM process can becontrolled. When no signal is present in the repeater pass-band, the AMprocess generates a signature signal buried deep within the noise. Whena signal is present, the signature signal can be used to uniquelyidentify the repeater.

In order to accomplish this, the following operations are performedwithin the repeater. The wideband signal w(t) or primary signalconstituting the signal to be repeated at the repeater is AM modulatedusing a narrowband signal of the form (1+r(t)), where for purposes ofthis disclosure r(t) is referred to as the second signal. The AMmodulated signal is then subject to any pre-existing methodology ofrepetition used at that repeater, generally expressed as a delay on thesignal followed by amplification.

The mathematical effect of this form of modulation is to generate aco-channel signal (e.g., the signature signal) w(t)r(t) in the repeaterbandwidth. The 1 in the term (1+r(t)) simply replicates the primarysignal (e.g., the mobile signal for uplink signals or the down link forbase station signals). Since AM modulation is equivalent tomultiplication, the modulation can also be viewed as multiplication ofw(t) by the function (1+r(t)).

To illustrate the concept further, consider a particular narrowbandchannel. In the narrowband channel, if an active mobile call usingsignal s(t) was in progress, the co-channel signal generated by the AMprocess will be of the form s(t)r(t). If the channel were inactive, theco-channel signal will be of the form n(t)r(t) where n(t) is noise. Bysuitably controlling the norm (or average amplitude) of r(t), themagnitude of the co-channel component can be maintained at a muchreduced power level with respect to the primary mobile signal s(t).Further, any spectral spillage into adjacent bins can be reduced belowthe noise power level in those bins by suitably manipulating theamplitude of r(t). Thus, the amplitude control of the signature signalsallows the amplitude of the signature signal to lie buried in thenaturally occurring noise that is present at the final destinationreceiver, i.e., the base station, the mobile appliance, or anothernetwork device.

By controlling the amplitude of the second signal r(t), both theco-channel signal component and the adjacent channel interference can bemade as large as or as small as desired. The amplitude control isdetermined based on the relative power desired between the primarysignal s(t) and the signature signal or co-channel component. After aproper determination is made, this amplitude is fixed at the repeaterduring operation. Generally the ratio of the primary signal and thesecondary signal is greater than unity.

Thus, for example in an active cellular channel, the introduced repeateridentification signal, the signature signal can be at a power level 9 dBor lower than the primary signal; whereas, in an inactive channel, thesignature signal will be 9 dB or lower than the preexisting noise inthat channel. In every channel, the corresponding signature signal ispreferably at a power level 9 dB or lower than the pre-existing signallevel in that channel. The 9 dB value is chosen simply to quantify theconcept and any other number can be selected with equal applicability.For a given primary signal s(t), it is apparent that the second signalr(t) distinguishes the particular repeater. Thus each repeater has aunique second signal r(t), which is a narrowband waveform.

The collection of such second signals r(t) over a set of repeaters,denoted S, may be drawn from sets of waveforms with specific properties.For example, the set S may be orthogonal, quasi-orthogonal, orshift-orthogonal. The properties of the second signals r(t) used togenerate the set S will, among other things, depend on the number ofrepeaters implemented in a cellular system cell or sector. Codesequences such as Golay-Hadamard and other sequences are equallyenvisioned when appropriate.

An aspect of the disclosed subject matter that needs to be highlightedis that the signature signal s(t)r(t) is formed as a function of theprimary signal and the second signal. The signature signal is not thesecond signal. The signature signal differs from other signature signalsbased not only on the particular repeater but also on the primary signalthat is input to the repeater. As shown in FIG. 7, the repeater 702receives a primary signal from the mobile appliance 701 or other networktransmitter. The primary signal s(t) is then multiplied by a function(1+r(t) where r(t) is a second signal unique to the repeater. The outputof the repeater is an aggregate signal s(t)(1+r(t)) including both theprimary signal s(t) and the signature signal s(t)r(t). The networkanalysis system 703 then receives and processes the aggregate signal asdescribed later to determine if the signal was received via a repeaterand, if so, determines the specific repeater.

FIG. 8 is a representation of an embodiment of a modification circuitused to create the aggregate signal from the primary signal. In therepeater 800, the receiver 801 receives and supplies the primary signals(t) to an A/D converter 802 and the digital signal is supplied to themodification circuit 810. The modification circuit includes a cyclicshift register 813, a signal multiplier 811 and a signal adder 812. Asillustrated, the cyclic shift register 813 and the primary signal areinputs to the signal multiplier 811. The primary signal and the outputof the signal multiplier 813 are connected to the inputs of the signaladder 812 and the output of the signal adder is connected to the D/Aconverter 803 which provides the analog aggregate signal to atransmitter 804. The cyclic shift register 813 provides a repeatingsequence r_(k)(t). The modification circuit could likewise be entirelyanalog or other combinations of analog and digital. The modificationcircuit shown is for illustrative purposes only and is not meant tolimit the scope of the present subject matter.

The repeaters may, either apply their identifying signals or signaturesignals, synchronously or asynchronously. A synchronous approach wouldrequire the repeaters to operate in unison with an extraneous clock butwould provide greater discrimination of the repeater at the locationsensor. The repeaters may also apply identifying signals in a repetitiveloop so that the waveforms r(t) repeatedly cycle.

FIG. 4 is a representative flow chart describing an embodiment of arepeater watermarking a primary signal. In the method 400, the repeaterreceives a primary signal s(t) as shown in Block 401. The primarysignal, as indicated earlier, can come from a mobile appliance as anuplink signal, a base station as a downlink signal, or from anothernetwork device such as another repeater. The repeater then creates asignature signal as a function of the primary signal and a second signalwhich is associated with the repeater. In the embodiment shown in FIG.4, the primary signal s(t) is multiplied by the second signal r(t) toobtain the signature signal s(t)r(t) as shown in Block 403. The repeaterthen transmits the primary signal s(t), or a copy thereof, along withthe amplitude controlled signature signal s(t)r(t) as an aggregatesignal s(t)(1+r(t)) as shown in Block 405. The second signal r(t) may bea code sequence.

The detection of the signature signal at the network sensor or receiveris formed from two hypotheses. The signal in a narrowband channel at thelocation sensor is either of the two hypotheses. Hypothesis 1: where thereceived signal is the primary signal s(t) plus noise; or Hypothesis 2:where the received signal is s(t)(1+r(t)) plus noise.

The network sensor or receiver determines which hypothesis is true andif Hypothesis 2 is true, identifies which r(t) in S is applicablethereby identifying the repeater used.

Since it is generally very difficult to search for the signature signalwithout first extracting the primary signal from the aggregate signalreceived, the signal recovery proceeds in two stages. An embodiment of amethod for signal recovery is shown in FIG. 5. The first stage is thedetection of the primary signal, and the second stage is the computationof candidate signature signals or candidate aggregate signals based onthe derived primary signal and all possible candidate second signals ofrepeaters from which the aggregate signal could be received from, i.e.,all of the repeaters in the set S or a subset of S within apredetermined propagation distance from the sensor.

A receiver receiving a signal (e.g., a mobile uplink signal) proceeds inthe following manner to determine whether the call was amplified by arepeater, and the identity of the repeater as shown in FIG. 5.

The receiver receives a signal, which may or may not be an aggregatesignal, as shown in Block 502. The signal received by the receiver maycome directly from a mobile or other system node in which case thesignal is not an aggregate signal. If the signal is received via arepeater then it is an aggregate signal. The network analysis systemextracts the primary signal as shown in Block 504, for example, bydetermining the signal waveform s(t) by methods known to those of skillin the art. Since the signature signal (if the signature signal exists)is below the noise level in the channel, this detection proceeds as wellas it would in the absence of the AM process. That is, the introductionof the signature signal s(t)r(t) does not compromise the detection ofthe primary mobile signal s(t) in any significant manner. The extractedprimary signal is processed to recover the data or voice information inBlock 505.

The system may then null out the primary signal s(t) from the aggregatesignal s(t) (1+r(t) plus noise as shown in Block 506. Depending on thenulling technique used, the purity of extracting the residual signals(t)r(t) will differ. In general, the result of the nulling process willbe to generate a noisy version of the signal s(t)r(t). An additionalsource of perturbation on the signal s(t)r(t) will result if the channelis filtered. However, this step of nulling out the primary signal is notnecessary for some embodiments of the present subject matter.

Having determined the primary signal s(t), it is possible to formulatethe candidate signature signals s(t)r(t) as shown in Block 508. Thepresent disclosure also envisions, for embodiments that do not null outthe primary signal, formulating candidate aggregate signalss(t)(1+r(t)). The possible second signals r(t) associated with repeatersin operational range of the receiver can be acquired and stored in anumber of ways known to those of skill in the art. The problem thenreduces to detection of the known signature signal s(t)r(t) (possiblyfiltered) in the aggregate signal s(t)(1+r(t)) plus noise (if notnulled) or detection of the known signature signal s(t)r(t) (possiblyfiltered) in the nulled aggregate signal s(t)r(t) plus noise as shown inBlock 510 where the primary signal is nulled. Detection of a knownsignal in noise is a problem that has been solved by numerous knownmethods and all applicable prior art methods are envisioned. If thecandidate signature signal s(t)r(t) is not detected or the candidateaggregate signal s(t)(1+r(t)) is not detected, Hypothesis 1 holds, thuseliminating the possibility that the mobile signal was operated on(e.g., amplified) by a repeater. If the signal s(t)r(t) is detected,Hypothesis 2 holds, and the particular r(t) that effected the detectionthen unambiguously identifies the repeater.

FIG. 6 is a representative flow chart for a method 600 for determiningif an uplink signal was received via a repeater according to anembodiment of the present subject matter. At the repeater 620 a primarysignal is received from a mobile operating in the service area of therepeater 620 as shown in Block 601. The primary signal is thenmultiplied by a second signal, for this embodiment, sequence associatedwith the particular repeater 620 as shown in Block 602. The primarysignal and the signature signal which is a function of the primarysignal and the sequence is transmitted as an aggregate signal to thebase stations and wireless location sensors within range of the repeateras shown in Block 603.

The waveform of the primary signal s(t) (e.g., uplink signal) isdetermined using known prior art methods as shown in Block 606. From thesignal waveform of the primary signal s(t), candidate signals, either acandidate signature signal s(t)r(t)′ or a candidate aggregate signals(t)(1+r(t))′ is calculated using the known second signals r(t). Thenetwork analysis or geolocation system then uses prior art methods todetect the candidate signature signals or candidate aggregate signals inthe uplink signal as shown in Block 608. If a candidate signal is found,then the uplink signal is received via a repeater and the specificrepeater can be determined by the associated sequence as shown in Block609.

Another embodiment envisioned by the current subject matter isimplemented with a primary and secondary receiver. In this embodimentthe primary receiver functions as normal to receive a first signal in acommunication system whether or not the first signal is from a repeateror other network device and thus whether or not the first signal is anaggregate or composite signal. As described previously, the primaryreceiver extracts the primary signal s(t) from the first signal w(t). Inaddition to recovering the data from the primary signal, the primarysignal is also provided to a secondary receiver.

The secondary receiver can be a separate receiver co-located at theprimary receiver or contained within the primary receiver. In eithercase the methodology is generally the same. The secondary receiver alsoreceives the first signal. Since the secondary receiver has both thefirst signal w(t) and the primary signal s(t) provided by the primaryreceiver. An inverse transfer function can be applied such that themodification, if any, to the primary signal s(t) will be revealed. Theexistence of the modification may be an indication that the signal wasoperated on by a repeater or other network device; and since eachmodification in the system is unique, the identity of the repeater orother network device can also be determined. A benefit of this latterembodiment is that the secondary receiver can be implemented as an addon, where the secondary receiver contains the hardware and software fordetermining the modification and is simply tapped into the existingprimary receiver to recover the primary signal.

No constraint exists on combining the scheme of this subject matter withother schemes to identify a repeater. For example, in a GSM cellularprotocol, a parameter termed the Timing Advance (TA) parameter may beused to identify the radius at which a particular mobile may be located.This TA parameter may be used jointly with the scheme proposed here toincrease the number of identifiable repeaters in a cell or sector.

While preferred embodiments of the present inventive system and methodhave been described, it is to be understood that the embodimentsdescribed are illustrative only and that the scope of the embodiments ofthe present inventive system and method is to be defined solely by theappended claims when accorded a full range of equivalence, manyvariations and modifications naturally occurring to those of skill inthe art from a perusal hereof.

1. A wireless communication system comprising: a plurality of basestations and at least one repeater, the at least one repeater comprises:a receiver for receiving a primary signal; a transmitter fortransmitting a first signal; a modification circuit for modifying theprimary signal into the first signal, the modification circuitcomprising: a cyclic shift register, a signal multiplier and a signaladder; the cyclic shift register and the receiver being connected toinputs of the signal multiplier, the receiver and output of the signalmultiplier being connected to inputs of the signal adder; and, theoutput of the signal adder being connected to the transmitter.
 2. Thewireless communication system of claim 1, further comprising an A/Dconverter between the receiver and the modifying circuit.
 3. Thewireless communication system of claim 1, further comprising a D/Aconverter between the modifying circuit and the transmitter.
 4. In acommunication system including a primary receiver, a primarytransmitter, and a repeater that applies a known modification to aprimary signal passing there through that identifies the repeater, wherethe primary receiver receives a first signal from the primarytransmitter either directly or via the repeater, and where the firstsignal includes a primary signal and, if the first signal is receivedfrom the repeater, also includes a secondary signal that is a functionof the primary communication signal and the known modification appliedby the repeater, the method of determining if a signal received by theprimary receiver is received directly from the primary transmitter orindirectly through the repeater, comprising the steps of: receiving thefirst signal at the primary receiver; outputting the primary signal fromthe primary receiver; receiving the first signal at a secondary receiverand obtaining the primary signal from the primary receiver; applying aninverse function of the first signal and the primary signal to retrievea modification; and determining whether the first signal has beenreceived from the repeater by comparison of the modification and theknown modification.
 5. The method of claim 4, wherein the communicationsystem is a wireless communication system.
 6. The method of claim 4,wherein the primary receiver is a network analysis system.
 7. The methodof claim 4, wherein the primary transmitter is a mobile unit.
 8. Themethod of claim 4, wherein the primary signal is a uplink signal.
 9. Themethod of claim 4, wherein the primary signal is a downlink signal. 10.The method of claim 4, wherein the known modification is multiplicationby a identification signal.
 11. The method of claim 10, wherein theidentification signal is AM.
 12. The method of claim 4, wherein theprimary signal is amplified such that the ratio of the primary signal tothe secondary signal is greater than unity.
 13. The method of claim 12,wherein the secondary signal is 9 dB less than the primary signal. 14.The method of claim 4, wherein the primary transmitter is a mobile unit.15. The method of claim 4, wherein the secondary receiver is a networkanalysis system.
 16. The method of claim 4, comprising the step ofnulling the primary signal.
 17. In a wireless communication systemhaving one or more repeaters, a first node and a second node, a methodof determining if a signal received at the first node is receiveddirectly or via one of the one or more repeaters comprising; creating,at the one or more repeaters, a composite signal w(t) that is a functionƒ(r(t),s(t)) of a primary signal s(t) received from the second node anda known identification signal r_(k)(t), where r_(k)(t) is unique foreach of the one or more repeaters; transmitting the composite signal tothe first node; detecting at the first node the primary signal s(t);determining an identification signal r(t) from an inverse functiong(w(t),s(t)) of the composite signal w(t) and the primary signal s(t),where g is the inverse of f; and determining if the signal is receivedvia the one or more repeaters based at least in part by theidentification signal and the known identification signals of the one ormore repeaters.
 18. The method of claim 17, wherein the knownidentification signal is AM modulated.
 19. The method of claim 17,wherein the function ƒ(r(t),s(t)) is s(t)(1+r_(k)(t)).
 20. The method ofclaim 17, wherein the inverse function g(w(t),s(t)) iss⁻¹(t)(w(t)−s(t)).
 21. The method of claim 17, wherein the one or morerepeaters are synchronized.
 22. The method of claim 17, wherein the oneor more repeaters are not synchronized.
 23. The method of claim 17,wherein the plurality of repeaters are synchronized.
 24. The method ofclaim 17 wherein the first node is a network analysis system.
 25. Themethod of claim 17 wherein the second node is a mobile unit.
 26. Themethod of claim 17, wherein the primary signal is a uplink signal. 27.The method of claim 17, wherein the first node is a mobile unit.
 28. Themethod of claim 17, wherein the second node is a network analysissystem.